AGB/post-AGB stars and white dwarfs
(Cioni, Gledhill, Napiwotzki)
Low to intermediate mass stars (0.8 to 8 solar masses) evolve between the Asymptotic Giant Branch (AGB), across the top of the HR diagram, to end their days as cooling white dwarfs. This is a transition that will be undergone by the majority of stars in the Galaxy, probably including the Sun, and these end phases of a star's life are characterised by huge mass loss, which is the major source of dust and chemically enriched material in the interstellar medium. During the final AGB stage, mass-loss rates can exceed 104 solar masses per year and can become highly asymmetric, resulting in the formation of circumstellar discs, bipolar outflows and jets, such as seen in the protoplanetary nebula AFGL 2688 (left). The most likely mechanism for this asymmetry is the interaction of the mass-losing star with a binary companion, or perhaps with a planetary system. The group studies these objects in the post-AGB phase using a variety of observational and modelling techniques. The final white dwarf cooling phase, that follows on from AGB envelope expulsion, may last up to billions of years. Investigation of these faint long-lived objects accordingly has the potential to reveal the character of star formation in the young Milky Way.